Progesterone receptor in the rat ovary: further characterization and localization in the granulosa cell

We have recently described a progesterone receptor in the cytosol of ovaries of hypophysectomized, estrogen-primed, immature rats. This progesterone receptor was shown to be a thermolabile, saturable protein, which is specific for progestins (R5020 and progesterone), and elutes at the void volume of a Sephadex G-200 column. In the present study, we performed a more detailed analysis of the biochemical properties of this receptor and examined its cellular localization within the ovary. Treatment of the ovary cytosol with protamine sulfate and N-ethyl maleimide abolishes the specific binding of 3H-R5020, indicating that the receptor is an acidic protein containing cysteine residues necessary for binding. Gel exclusion chromatography shows the progesterone receptor to have a mean Stokes radius of 86 A and a molecular weight of approximately 300,000 daltons. Kinetic analysis indicates that the receptor--R5020 complex dissociates very rapidly, with a t1/2 of 10 minutes. The cytosol of isolated granulosa cells bind 3H-R5020 specifically, demonstrating that the ovarian progesterone receptor is present in the granulosa cell.